Your engine is roughly making 250-260HP with that you have listed. Appx 200 at the wheels give or take. 1/4 mile you would probably run mid 14s give or take again depending on, 5 speed or Auto, drag radials or street tires, traction issues. etc. As for Nitrous I have no clue, never messed with it. Id say a 50-75 shot would be pretty safe, but thats just a guess
The Explorer stuff isn't exactly the greatest HP maker, wasn't really designed to be. It's more of an inexpensive mild upgrade. To get to 300 at the wheels you'll need a better combo. On a 302 most use a TFS top end kit (heads, stage 1 cam, street intake, etc.) or AFR 165's, Custom Cam, Edelbrock Intake, etc. Something along those lines.
I'd say your current combo is around 250-270 roughly, should run in the high to mid 13's on street tires. You could throw a 100 shot on it but make sure you have the fuel & ignition upgrades so you don't blow it up.